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SES OF DISEASE IN YOUNG SALMONOIDS 



From BULLETIN OP THE BUREAU OF FISHERIES, Volume XXVIII, 1908 



Proceedings of the Foiirth Intertiaiional Fishery Ctnigress 



Washington, igoS 




WASHINGTON :::::: GOVERNMENT PRINTING OFFICE 




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CAUSES OF DISEASE IN YOUNG SALMONOIDS 



From BULLETIN OP THE BUREAU OF FISHERIES, Volume XXVIII, 1908 
Proceedings of the Fourth International Fishery Congress : : Washirigton, igo8 




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WASHINGTON :::::: GOVERNMENT PRINTING OFFICE 



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BUREAU OF nSHERIES DOCUMENT NO. 689 
Issued April, 1910 






CAUSES OF DISEASE IN YOUNG SALMONOIDS 

By Eugene Vincent 

Fish Culturist, Aquarium of the Trocadero, Paris 

Paper presented before the Fourth International Fishery Congress 
held at Washington, U. S. A., September 22 to 26, 1908 



CONTENTS. 

j» 

Page. 

Diseases of the gills 909 

Faulty hatching equipment and conditions 909 

Measures of prevention 912 

Curative measures 914 

An epidemic of "staggers" in rainbow trout fry 914 



CAUSES OF DISEASE IN YOUNG SALMONOIDS. 

By EUGENE VINCENT, 
Fish Culturist, Aquarium of the Trocadcro, Paris. 

[Translated from the French.] 

The common trout and its varieties are especially subject to disease of 
the gills, and other salmonoids likewise are not exempt from it. Such disease 
consequently presents great difficulty to fish culturists, who must find means 
of combating it. Another frequent trouble is the epidemic which may be 
called "staggers." The effective measures in both cases are those of preven- 
tion rather than attempt to cure; and the best means of prevention is perfect 
cleanliness of equipment, from the beginning of the hatching period throughout. 
To maintain the necessary cleanliness, however, is a question of style of appa- 
ratus as well as unremitting care. 

DISEASES OF THE GILLS. 

FAULTY HATCHING EQUIPMENT AND CONDITIONS. 

As fish culturists well know, the styles of apparatus for incubating eggs 
of the salmon species are very numerous. In France the most common equip- 
ment is the Coste trough and its derivatives, consisting of a kind of rectangular 
zinc box 0.50 to 0.60 meter long, 0.25 meter wide, and 0.20 meter high, with 
two partitions of perforated sheet iron, the one serving to admit the water 
from below, the other allowing it to pass out from above. Into this box is 
set a glass grille of dimensions to fit. 

I have heard much in praise of all varieties of apparatus, but I have heard 
little concerning their disadvantages and dangers. It is of these latter that I 
shall speak. 

First of all, I consider the equipment bad which does not allow the fish 
culturist to see what is taking place below the grilles on which the eggs are 
resting or permit of cleaning without disturbing the eggs. 

We are told that there are currents of water in this apparatus, which 
receive as much as one-half liter of water per minute. There can be no currents 
of water in these troughs, however, especially in those with partitions; there 
is, to be sure, a change of water, but there is no current which would bring 
about a flow throughout, and this may be easily shown by putting into the 
water coloring matter or thin strips of paper. And it is precisely the absence 

909 



910 BULLETIN OF THE BUREAU OF FISHERIES. 

of this current which determines and creates the dangers to which the eggs 
and the fry are exposed — this, first, because the quantity of water suppUed to 
the apparatus is not sufficient; second, because all obstacles, as the partitions 
in the apparatus, operating to prevent a current, become a hearth of infection 
of all kinds, by the comers they make; third, because of the very dimensions 
and the shape of these troughs; and fourth, the visible proof, because there 
are found in these troughs and in the rearing troughs fry large enough to be 
able to maintain an equilibrium, yet lying on their sides, with gills compressed 
against the bottom of the basin and in contact with the slimy ooze of the bottom. 
If the fish makes a movement, it is only to fall back on the other side, so that 
the gills are by turn infected with noxious substances from the bottom, which 
can not be seen and cleaned as it ought to be. 

The greatest cleanliness is always necessary in fish culture, and it must be 
made attainable. Let us see, without being pessimistic, what the conditions 
most often are. 

The fish-cultural apparatus found on the market has not all been invented 
by fish culturists having a knowledge of this science. The manufacturer sells 
apparatus the advantages of which he extols with the aid of so-called fish- 
cultural tracts (though in reality they are not such), and the inexperienced 
purchaser establishes his business immediately, with confidence of success. 

If he buys eyed eggs, he will not have the same difficulties as the man who 
collects the eggs himself. Let us take the latter for example. The eggs are 
placed on the grilles and the grilles in the troughs, all these things being more 
or less well washed, but the wooden screens can not be put in the flame so as to 
destroy all germs. Then there may be among the eggs excretions of fishes 
that may have fallen in the stripping, or there may be shells of broken eggs, 
all of which may drop through the grille to the bottom of the trough, to be left 
there during the entire period of incubation, together with any dead eggs that 
may have slipped between the glass bars. 

If the water contains sediment, this will be deposited on the bottom of 
the trough and will remain there. The fish culturist has been told that all he 
has to do is to take out the few dead eggs and await the hatching of the 
others before cleaning out his apparatus. Water is not the same everywhere; 
all has its advantages and its disadvantages; in France the incubation takes 
place in water the temperature of which varies during this period from 
6° to 12° C. (I do not refer to the mountain region), and often the incubation 
period lasts from forty-five to fifty days. It is well known that some eight 
days before the first hatching some eggs will burst. Their contents, escaping, 
spread over the eggs in long filaments which attach themselves to the grill, 
pass through it, go to the bottom, increase the amount of sediment, and 
encourage the invasion of Saprolegnia. 



CAUSES OF DISEASE IN YOUNG SALMONOIDS. 9 II 

The unfertile eggs are not taken out, and the first filament of fimgus may 
not be seen on an egg that is in a comer of the grill. But later the eggs may 
be covered with this delicate down, and although something might still be done 
for the embryos whose breathing is thus interfered with, even the flow of water 
has not been increased since the eye spots appeared, and so the fungus establishes 
itself. 

The hatching time is now at hand, and may last, in water having a tem- 
perature of 10°, some ten or twelve days, and sometimes more. Until it is 
over there is no thought of placing the fry in a cleaner place. As the fry hatch 
they fall, like the shells of their eggs, to the bottom of the trough, on a soft 
velvet composed of the flourishing Saprolegnia. 

And these unfortunate fry, the gills of which have never ceased being in 
forced contact with all the impurities and disease germs which line the bottom 
of the trough, are now to be disturbed in this water, the sediment in which will 
be visible to the operator when he shakes or moves the trough. Nor is it only 
the breathing apparatus which suffers, but the entire fish, for its body receives 
shocks and wounds, inviting the fungus, and the mouth particularly becomes 
infected. 

The disease then has secured its hold. It is not perceived, for the operator 
believes that he has done all that is necessary by cleaning the fry at the close 
of the hatching. They may have been replaced in the same trough after giving 
the latter a hasty cleaning, for maybe there was no other at hand. Fry from 
two different troughs may have been put together without thought of the 
imprudence of this. The lots are then of different ages by ten to twelve days, 
and they are a little crowded, there being 2,000 to 2,500 in those little troughs 
without any increase of the flow of water — for how long? They will be fed in 
a month, perhaps six weeks. In the meantime there is amusement in finding 
a few monstrosities among them. These die from day to day and the yolk 
sac sheds its contents, which adhere to the bottom and form white spots which 
occasion no alarm. The Saprolegnia finds again a favorable bed for development. 

The oldest and most robust of the fry, endeavoring to move about a little, 
reach a corner of the trough, where they crowd against each other. By their swim- 
ming movements they form in this corner a small current, or more exactly, a 
slight motion of the water sufficient to maintain them in equilibrium on their 
yolk sacs facing this small partial current. As soon as the fry ceases to feel this 
current it can not maintain itself on its yolk sac and falls on its side. Is it no 
longer so strong? No; that is not the reason — it is the motion of the water 
which is lacking and which does not exist in the trough in any other spot except 
where the fry make it themselves. The proper motion of the water is created 
by a device of mine which I shall describe, a siphon outlet system ; but for the 
present I say that the eggs in incubation were not given a current sufficient to 
wash them, facilitate the exchange of gases, and keep them from being covered 



912 BULLETIN OF THE BUREAU OF FISHERIES. 

with a thin layer of sediment. I maintain that thus the embryos also suffered, 
and I am sure that it is in this way the fry contract the disease of the gills. 

Such is the origin of the disease which manifests itself in young fish in 
swollen gills, impregnated with dirt and bulging so much as to push out the 
operculum. The fish are seen to weaken and turn dark in color and then die, 
at first in small numbers, but increasing to an almost complete mortality. It 
may be justly assumed that those which escape are those which hatched last 
and have not been so long in contact with the deposit on the bottom of the 
trough. This terrible disease may not manifest itself among the yoimg fish 
until the age of five to six weeks. 

In addition to the cause I have named for the origin of this disease of the 
gills, it is sometimes due to placing too much food into the rearing troughs. 
The coagulated blood, spleen pulp, pulp of liver, etc., becoming diluted, render 
the water at times so tinted that it is impossible to see through it. The gills 
are impregnated with putrefiable matter, which soon gives rise to this terrible 
epidemic, especially if the water is not aerated and frequently changed. 
Lastly, a great number of fry in a small space, not receiving a sufficient quantity 
of water, acquire the disease of the gills by atrophy, as may be easily recognized 
by the small size and emaciation of the fish. 

MEASURES OF PREVENTION. 

As stated at the outset, the remedy for this disease is prevention, which 
involves the utmost care on the part of the attendant, with also the form of equip- 
ment which shall permit of the most perfect cleanliness. I will indicate the 
means I have employed and consider essential. 

1. Discard all apparatus that does not allow the interior to be examined. 
It must be possible to see under the grilles on which the eggs are placed, and, if 
necessary, to clean the bottom of the trough without interfering with the 
incubation process. 

2. Use an equipment which will permit of retaining the fry therein after 
the hatching is over. Discard the wooden grille frame for one of metal and 
replace the glass tubes with solid glass rods. 

3. Have an ample supply of water in proportion to the number of eggs in 
the trough, and create currents to reach every part. Increase the supply of 
water, if possible, as soon as the eye spots appear in the egg. 

4. Do not crowd the eggs on the grille. Takeout the dead eggs each day. 
Do not refill the spaces left by the removal of dead eggs. These, taken out to 
prevent their bursting in the trough, will now give more space to the developing 
eggs. Take out any eggs containing monstrosities. 

5. Give a thorough cleaning both to grilles and troughs when the eggs are 
ready to hatch, so that the fry may fall to the bottom of the trough without 
danger to their gills. A hand siphon cleaner « should be used for the trough. 

"Vincent E.: Devices for use in iish hatcheries and aquaria. Proceedings Fourth, International 
Fishery Congress, Bulletin U. S. Bureau of Fisheries, vol. xxviii, 1908, p. 1030. 



CAUSES OF DISEASE IN YOUNG SALMONOIDS. 913 

6. If the hatching equipment is not adapted for retaining the fry, transfer 
each day's hatch, classifying by age, to thoroughly cleaned troughs, with such 
number to each trough as may be held for five or six weeks. In making the trans- 
fer use a syringe of i X to i K liters capacity, with a tube of 0.0 1 7 meter diameter, 
so that the gills and yolk sac of the fry shall not be compressed. Do not keep 
the fry in darkness or obscurity; daylight is better for them. Eliminate mon- 
strosities. Change the water every day, the siphon outlet" serving also as an 
auxiliary cleaner, since it creates currents in the troughs. Dispose the intake 
at a point to produce a longitudinal motion of water. 

7. I feed the fry, to aid them in developing, beginning four days after 
hatching. This has been my practice for some six years, and I have found it 
good. I clean the troughs every day with a brush, called codfish tail, and take 
out any remnants of food which the siphon outlet has not carried off. When 
the fish are some five or six weeks old I put them in large troughs, the cleaning 
of which is simpler, and here I feed them with beef spleen placed in small wire 
baskets fixed at about mid depth of the trough, this to prevent the fish from 
seeking food at the bottom and so that less shall be wasted. 

It is difficult in a large establishment to have really filtered water. No 
filter at all is better than a bad one. 

Various devices of mine described elsewhere (op. cit.) have proved an aid to 
the realization of the necessary cleanliness in fish hatching. I have adopted 
also a combination trough, to be used both for the eggs during the incubation 
period and for the fry afterwards, thus avoiding the disturbance and injury of 
a transfer of the very young and delicate fish, while at the same time offering 
the advantages of the currents they need, besides facilities for perfect cleanli- 
ness. This trough is of cement and measures inside 1.5 meters long, 0.3 meter 
deep, and 0.35 meter wide. The shape is such as to aid in cleaning, having no 
angles, but curves only. The size is sufficient to accommodate two grilles and the 
siphon outlet apparatus already referred to. The interior is especially designed, 
after repeated experiment, to provide currents suitable for the eggs during 
incubation and later for the fry, to give the latter means of equilibrium and also 
supply them with food in a natural manner. The particles of food are always 
in motion in this trough. The model belongs to the firm of Leune, Rue Cardinal 
Lemoine, 28 bis, Paris. 

It is important for the fry to be in equilibrium, and not lying with gills 
against the bottom, even though the troughs be clean, a condition which is 
attainable if there be a current, but not otherwise. As soon as there is the 
smallest motion giving the sensation of a current even the very young fry will 
respond to it. This may be tested by the simple experiment of using a syringe 

o Vincent, op. cit. 
B. B. F. J 908 — s8 



914 BULLETIN OF THE BUREAU OF FISHERIES. 

in the water close to the fry. The Httle heads at once turn toward the current, 
the bodies righting themselves upon the yolk sac, and this equilibrium is main- 
tained so long as the current continues. When it fails the fry fall back on 
their sides. 

It is suitable currents that also make it possible to feed the very small fry 
without danger of disease. Even before the yolk sac has begun to diminish 
they will face the currents and make efforts to catch small particles of food 
passing some three or four centimeters above them. I have shown this very 
interesting and amusing sight in aquaria, and it is because of such experiments 
that I insist the fry shall be fed when four days old. At the end of ten or twelve 
days, in water having a temperature of about 10°, will be observed the occur- 
rence above noted, and a few days later these fry, developed and strengthened 
by the food they have had, but still with their yolk sac, may be seen swimming 
progressively. The fry should not be kept in darkness. They must be able to 
see their food to get it. 

CURATIVE MEASURES. 

With the precautions I have enumerated the fry will not be affected with 
the gill disease. If, however, I should find myself confronted with it I would 
reduce the number of fry by half; I would place them in semiobscurity and 
would give them no food for several days, in order not to put into the water 
the slightest substance for putrefaction, and keep the gills free of any organic 
matter due to the food or its remains. I would have well-aerated water and 
take care not to leave any dead fish in the troughs. Such would be the treat- 
ment to be given — a thorough cleaning from the beginning of the disease. But 
I do not guarantee that I could save fry which were seriously affected. 

The gills are very sensitive to the disease, and their impregnation with 
organic matter, be it only a temporary one, causes death. I have been a 
professional fisherman, and all fishermen know very well that fishes caught 
during the first days of rising water never live, can not live, even if they are 
taken with the most inoffensive of fishing devices, and this is so because their 
gills are filled with organic matter and sediment which rising water always 
carries along. Three or four days after the beginning of the rise of water the 
gills are slowly cleaned and the fishes live. 

AN EPIDEMIC OF "STAGGERS" IN RAINBOW TROUT FRY. 

The brood trout in this case weighed about four ounces and laid eggs now 
for the second time. The eggs were placed in filtered spring water at a tem- 
perature of 9°, 10°, and even 11°, and incubation lasted forty days. The 
greatest hatch took place on March 14, 1906, lasting two days. The small 
fry were placed in nonfiltered water, where they were kept from March 16 to 
April 14. 



CAUSES OF DISEASE IN YOUNG SALMONOIDS. 9^5 

These fry were fed regularly every day, from the fourth day after hatching, 
with pulp of beef spleen, first crushed in a mortar, then passed through a horse- 
hair sieve. Somewhat later I contented myself with rubbing the spleen pulp, 
which was somewhat diluted, in the trough and between my hands, the fry 
eating this very well. On April 20, i. e., about thirty-five days after hatching, 
the trout, now in a pond, were eating pulp which I did not crush, but placed 
in a small basket suspended between two currents in the pond. 

The pond was supplied with river water, of a temperature of i2>^°. It 
was 7 meters in length, 2.5 meters in width, and 1.8 meters in depth. The 
flow of water was 10 liters per minute from the town supply. There were 
9,000 fish. Time passed and these trout, having in only one and one-half 
months reached a size varying between 0.032 and 0.035 meter long, were well 
and healthy. 

We had reached April 24 when two things happened to cause me appre- 
hension. The allowance of food given to these trout had been gradually dimin- 
ished, and on the other hand the water flowing into the basin, at the rate of 10 
liters per minute, passed through a gravel filter, which did not inspire any 
confidence in me. 

Before reaching this filter the water passed through three decantation 
basins, each containing about 10 cubic meters, then it rose between two walls, 
where it met a filter composed of medium pebbles, a layer of 0.25 meter, then 
a similar layer of gravel, then another layer 0.3 meter thick of finer gravel, 
then coarse sand 0.15 meter thick, and finally a layer of 0.15 meter of fine sand. 
These layers of gravel and sand were separated from each other by suitable 
sheets of metal. 

Being able to see from the side into the interior of this filter, through glass 
panes 0.027 meter thick and i meter high, I ascertained that the filter was in 
reality dirty, the dirt obstructing the passage of the water through the gravel, 
so that the latter was kept back and rose in the basins of decantation. (It is 
well known that a filter made of gravel and sand does not operate well until 
it collects a surface layer of dirt, but on the other hand, as is not so well known, 
it is not necessary to wait until the surface is dirty to have the under layers 
cleaned.) I saw then that at hundreds of places organic matter formed with the 
gravel a more or less compact mass, and mold was to be found everywhere. This 
organic matter, this mold, consumed the oxygen contained by the water to the 
detriment of the welfare of the rainbow trout. 

I foresaw danger in this growth of Saprolegnia of all kinds, and the multi- 
tudes of small animal life, some of it almost invisible to the naked eye. 

The water was cut off and the upper part of the filter was partly cleaned; 
not thoroughly, however, as both time and space are needed for the washing 



9l6 BULLETIN OF THE BUREAU OF FISHERIES. 

of all the gravel and all the sand, the layers of which lay flat on an area of 2.4 
meters by 0.6 meter. 

The filter, in short, was not sufficiently cleaned, the water was turned on 
again, and not sufficient note was made of the fact that it was the 8th of May 
and the river water at a temperature of 17°, the first result of which would be 
a sudden mortality among the trout. This happened, too. From May 8 to 
May 17 the water was maintained at this temperature, and on the morning of 
the last day I noticed some 30 trout dead in the pond, while the others were 
being carried to the grating at the outlet. Most of the fish turned over and over 
and made pirouettes, then jumped into the mass of water as if to cross it in one 
movement, but they fell exhausted and dropped to the bottom. About 11 
o'clock in the morning 300 trout were dead. 

The fish had " the staggers." In two days they grew somewhat dark, then 
they began to weaken, swam with difficulty, and could no more maintain a 
horizontal position; their behavior was abnormal, and they finally died. All 
of the trout did not show the weakening, but fell to the bottom of the pond 
and succumbed after opening their gills convulsively two or three times. 

I gathered the dead trout with a net and counted 1,200 of them. That 
evening there were more on the bottom of the pond, and by the evening of the 
next day the mortality was almost complete. The remainder living was an 
insignificant number. I believe that 160 were placed in spring water, and out 
of these 160 only about 100 were saved. 

This mortality had been caused by the imperfect action of the gravel filter 
and by its dirtiness, by the fermentation of the organic matter which the filter 
had retained when from April 24 the temperature of the water, 12°, rose to 
17° about May 10. The cleaning of the upper layers of fine sand of the filter 
gave free passage to the Saprolegnia, the mycelium of which abounded in the 
lower parts or layers of gravel, and all this infection invaded the basin, with the 
effect of all as just described. 

In order to remedy this at least partially, if there is no spring water at 
one's disposition, it is better not to use any filter than to use such as this. The 
great quantity of water necessary in a fish-culture establishment makes it 
difficult to obtain a perfect filter. It might be well to use water from a river, 
easily aerated if the pond is lower than the river. 

The best means of doing without a filter would be to keep a small fry 
trough very clean, so as to be susceptible only to disease or an infection coming 
from without, which is much at best. In order to attain this practical result, 
a siphon-outlet system, of a kind such as I have devised (op. cit.), should be 
installed. 



